What happens to the brain when we forget?

Brain studies could help with Alzheimer's treatment

Scientists from Johns Hopkins used MRI's to find the underpinnings of forgetfulness that happens as we grow older. The new findings could help with treatment of Alzheimer's disease.

According to the research findings, forgetfulness is not just about memory overload. Forgetting where the keys are, where the car is parked, or the name of a new acquaintance is the result of deterioration of an area of the brain that stores memories, known as the hippocampus that degrades with aging.

Michael Yassa, assistant professor of psychological and brain sciences in Johns Hopkins' Krieger School of Arts and Sciences says, "As we get older, we are much more susceptible to 'interference' from older memories than we are when we are younger."

Instead of being able to learn new things, it becomes easier to revert to older memories. Yassa adds, "Maybe this is also why we tend to reminisce so much more as we get older: because it is easier to recall old memories than make new ones,"

MRI scans shows difference in younger and older brains

For the study, researchers used three different types of MRI scans to observe healthy young and older brains. Participants were either college students or 60 to 80 year olds.

The different MRI scans showed the researchers about the structure and functional capacity of the brain.

Yassa explained, "Our research uses brain imaging techniques that investigate both the brain’s functional and structural integrity to demonstrate that age is associated with a reduction in the hippocampus's ability to do its job, and this is related to the reduced input it is getting from the rest of the brain."

Functional, structural and diffusion MRI's that track molecular movement were used in the study.

The researchers compared how college students process new information, comparing to older adults, age 60 to 80.

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In the study, they were asked to identify objects from photos as either “indoor or outdoor” by pressing a button. Some of the images were similar, some identical and others, completely different. The MRI’s were used to view how the participants classified the objects.

A few minutes later they were asked to classify pictures as “old or new”.

Yassa explained younger participants classified all the pictures as “new”, but the brains of older adults struggled with new input.

"Pictures had to be very distinct from each other for an older person's hippocampus to correctly classify them as new. The more similar the pictures were, the more the older person's hippocampus struggled to do this. A young person's hippocampus, on the other hand, treated all of these similar pictures as new.”

A crucial finding was older adults struggled to recognize items that were “similar”, said Yassa. Older individuals classified fewer of the images as similar. Instead, they had more “old” responses.

The finding indicates degrading function in the hippocampus, known as the "perforant pathway”.

Clearer understanding of memory loss

"We are now closer to understanding some of the mechanisms that underlie memory loss with increasing age," Yassa said. "These results have possible practical ramifications in the treatment of Alzheimer's disease, because the hippocampus is one of the places that deteriorate very early in the course of that disease."

The study helps scientists understand how the brain works with aging and what happens when we forget. The series of experiments show distinct differences in how the aging memory processes new, old and similar items.

For older adults, it’s easier to retrieve stored information and more difficult to process new information because memory pathways in the brain degrade over time. The finding could help with Alzheimer's disease treatment.